Listen

Copyrightopen university

Read

InterviewerMark, ice doesn’t behave the same way at the different poles, does it, so how does it vary?

Mark BrandonWell one of the things that affects the ice most of all is the basic geography.In the Arctic you’ve got land and then a deep ocean in the middle, whereas in the Antarctic you’ve got land in the middle and deep ocean around the edge.If you go back to the Arctic, in winter all of that Arctic ocean gets frozen over with what we call sea ice.Which is a very thin layer of ice only perhaps two or three metres thick.It extends out, about 15 million square kilometres of the ocean gets covered by this sea ice.And it’s a bit like if you think of polystyrene floating on the sea, it gets blown about by the wind, so the sea ice is constantly moving and constantly drifting around and grinding up.So if you hear about ice being thicker than three meters, it’s usually two ice flows three metres thickness that have bumped into each other one on top of the other.

InterviewerYes, so all the bits of floating ice in the Arctic, it does collide, I would imagine, forms ridges, does it?

Mark BrandonIt does, and if you actually go online, there’s the International Arctic Ocean Buoy project, IOEB, and you can actually look at the drift tracks of buoys that are actually up there right now sending back weather data from the Arctic Ocean that drift with the sea ice.And so you can look at these fantastic movies of how the ice drifts.

InterviewerHow does ice behave in the Antarctic, not in the same way then?

Mark BrandonWell the seasonal change between the Arctic, in the Arctic, about two-thirds of the ice disappears between the summer and the winter, but in the Antarctic, almost all of the ice disappears in Antarctic summer.

InterviewerAnd where does it go to?

Mark BrandonIt melts away.So there are only a couple of small areas, mainly the Ross Sea and the Weddell Sea, and quite close to the coasts.When I say most of the ice disappears, there are about two million square kilometres of ice still in the Antarctic, but compared with Antarctic winter, that two million square kilometres of ice grows another 15 million square kilometres, so it really is just the remnants of a vast amount of ocean covered by ice.

InterviewerAnd we’re talking about, for the permanent ice, we’re talking about some incredible thicknesses as well, aren’t we, in the Antarctic particularly?

Mark BrandonWell if you look at Antarctica, Antarctica is a continent.It’s land and then snowfall over millions of years gets compressed and turned into ice, and individual layers of this snow build up thickness of ice.And this started happening, this snowfall, maybe 35 million years ago, and the thickness of ice now on East Antarctica, the east part of Antarctica, is about three kilometres thick, and that’s made entirely of snow, and so it’s fresh ice.It’s the sort of stuff that you, you know, when it reaches the edge of the continent, this land ice, it can either form an ice shelf, which is a large, thick shelf of ice, of perhaps two or three hundred metres thick, or it can, the glaciers can fall straight into the sea and form icebergs.Whereas the sea ice is just frozen seawater, and so anything that’s in the sea water gets trapped within the ice.And it’s quite a porous thing, sea ice, compared with land ice, because it’s formed from ice crystals growing in the water rather than snow fall being compressed.

InterviewerSo there’s life within the sea ice?

Mark BrandonThere is.Anything that’s within the sea water, for example phytoplankton and algae, they get entrained within the sea ice as it actually grows.And in certain parts of the Arctic, for example, the sediment gets entrained within the ice too, so you get dirty ice.Sediment gets trapped within the ice.So anything in the sea water gets trapped in the ice as it actually grows.

InterviewerWell I've seen some remarkable photographs you’ve taken of brown ice, which is what happens when perhaps the ice melts and the water around it becomes brown.What is that, are those organisms?

Mark BrandonYes, usually in the ocean, the surface layers of the ocean are quite depleted in nutrients, because lots of biological production is going on, whereas in places like the Antarctic, the strong winds cause water from a deeper part of the ocean to rise towards the surface.They’ve got lots of nutrients in them, so it means the biological production can be incredibly high in certain specific locations.When that happens, the diatoms and phytoplankton in the water can grow enough to make the water actually seem chocolaty brown.

InterviewerWhat happens when these creatures are trapped within the ice?I mean surely it would just freeze them and they cease functioning.

Mark BrandonWell, they're thermophiles, so they can actually live within the matrix of the ice structure.In the Antarctic, the ice is probably only a couple of metres thick, well probably it is only a couple of metres thick, and so most of that biological material is, or biological activity is just in the bottom ten or so centimetres of the sea ice.In the Arctic, where the ice is a bit thicker, you actually get different sorts of species live quite at the bottom of the ice where the water’s quite salty.The further up the ice you go, the salt decreases because the salt drains out as the sea ice grows.By the time you get to the surface of the ice, there are species that can exist almost in the freshwater, in the melt pools on the top of the sea ice above the water.

InterviewerAnd if these are plants, are they photosynthesising in the same way that green plants do?

Mark BrandonThey do photosynthesise the same way, but they use a different pigment, so yellowish and browny rather than greeny coloured.

InterviewerHence this brown sea when the ice melts.

Mark BrandonExactly, and the brown colour.One of the interesting things is when the ice breaks up of course, that releases the algae, high algae concentrations back into the ocean, which of course is available for other animals to exploit.

InterviewerAnd perhaps one of the commonest animals that we think of are the krill, the shrimp like creatures.

Mark BrandonKrill are a euphausiid, a shrimp like creature; amazing animals in that they can live for several years, a living animal that can go up to maybe six, seven centimetres long.And the lifecycle of krill, they actually live quite close, at certain times of the year, quite close to the bottom of the sea ice and graze on the algae on the bottom of the sea ice.Now a few years ago some colleagues, myself and some colleagues from Southampton University and St Andrews University sent a robot beneath the ice which had a sonar system on it, and the sonar system was looking upwards, so we could look at the concentration of krill beneath the sea ice.And that had never been done before.

One of the problems with doing that sort of work is usually if you want to find out how much krill there are in the ocean, you have a ship on the surface of the sea, it fires sonar down into the water, and you can measure the krill.But if you take your ship into the sea ice, because the krill live quite close to the ice, the ship knocks all the ice out the way and it disturbs the environment.So by sending the robot beneath the ice looking upwards, it was a totally undisturbed environment.

InterviewerAnd what did you find?

Mark BrandonWell what we found was in a band about ten kilometres inside the ice edge, that the amount of krill in the area we were working was three times higher than what it was in the open ocean, so vastly greater inside the sea ice.The further you went into the sea ice it appeared to drop off, but we didn’t go as far as we could on that experiment because of technical limitations.But the biologist colleagues that I was working with, they thought that there was a thing called risk balancing going on.Where the krill, if they live quite close to the edge of the sea ice, as the ice breaks up it’s releasing this algae into the water so they can feed, then they do really well from feeding on this algae, and then because they're inside the ice edge, their main predators, which are things like whales and seals, they don’t want to be too far from the open water.So the further they are from the ice edge, perhaps the safer they are.So maybe it’s an evolutionary adaptation.

InterviewerThat’s interesting.And of course as this ice edge changes, presumably the distribution of the krill change?

Mark BrandonIt is.In summer, as the sea ice disappears, because like I said earlier most of the sea ice in the Antarctic disappears, they're essentially an open water species then, and they diurnally migrate down to 7-800 metres during the daytime and come up towards the surface at night.But they also get taken in ocean currents away from Antarctica.And there’s a particular, well Antarctica if you think of it, it’s a bit circular, and there’s one finger of Antarctica which points northwards called the Antarctic Peninsula, and that’s one of the main breeding grounds for krill.But just downstream from the Antarctic Peninsula, about 700 miles, is an island called South Georgia.

So when the sea ice goes away from the Antarctic Peninsula, krill that are at the top of the Peninsula, they drift towards South Georgia, and there it’s an island, they get trapped in the ecosystem of the island by the ocean currents and exploited by very high predator populations there.

InterviewerWell the population of seabirds and seals on South Georgia is legendary almost, isn’t it?This is a very rich area biologically.So are these all based on a foundation of krill?

Mark BrandonThey are based on a foundation of krill, and legendary, it was actually, it’s no accident that South Georgia was the centre of the whaling industry in Antarctica for about fifty years until they killed nearly all the whales.But the whaling stations of course are still on the island, you can go and see them now.But they get, the krill get brought up towards the island.They get trapped in the ecosystem by the ocean currents.The animals then don’t actually have far to migrate from where they're breeding, which is South Georgia, where you’ve got St Andrew’s Bay on South Georgia, there’s perhaps a quarter of a million king penguins.You’ve got hundreds and hundreds of thousands of fur seals all breeding.They have a short trip out to the shelf edge of South Georgia where they can feed on krill which are transferred into the region.

InterviewerAnd are they feeding directly on the krill, or are they feeding on fish attracted by the krill?

Mark BrandonAlmost all of them feed directly on the krill.One of the features of polar food chains is they're very short.You’ve got phytoplankton, krill and then higher predators, such as different types of seals, seabirds, squid and whales, so a very short food chain.In more temperate oceans, like the Pacific or Atlantic, there are maybe five, six, seven stages that the food chain will go through before you actually get to the higher predators, which means that Antarctic food chains and Arctic food chains are very efficient for transferring material from small things to very big.

InterviewerBut very dependent on those few links, that’s the problem.So if krill disappears or fluctuates then it affects the things that feed on it.

Mark BrandonExactly!One of the projects I've been working on for a few years with colleagues from the British Antarctic Survey is the amount of krill around South Georgia.I'm a physical oceanographer, polar oceanographer, so I'm interested in studying the ocean currents.The biologists are interested in the krill, and of course when the ocean currents are varying, different amounts of krill will come to the island.And what they’ve measured is vast differences in, between years, interannual variability in the amount of krill on the island.Some years there can be a huge amount; some years there can be hardly any.And of course being such a short food chain, when there are lots the animals do fantastically well; when there aren’t lots, then it is, a physicist would use the word carnage, but a biologist would be a bit more careful with how they use, the animals do very poorly and the populations don’t do very well.

InterviewerBut a lot of animals I suppose in the Arctic have, they live for quite a long time, so presumably that’s a way of riding out these fluctuations.

Mark BrandonThat’s what they think, yeah, exactly.You know, the species tend to be long lived and have lots of breeding cycles.So if any one breeding cycle isn’t successful, it doesn’t affect the wider species.The issue you're having in certain areas of Antarctica now, like the Antarctic Peninsula, is the environment is changing around the animals.

Copyright information

Feeds

If you enjoyed this, why not follow a feed to find out when we have new things like it? Choose an RSS feed from the list below. (Don't know what to do with RSS feeds?)
Remember, you can also make your own, personal feed by combining tags from around OpenLearn.

The Open University

The Open University is incorporated by Royal Charter (RC 000391), an exempt charity in England & Wales and a charity registered in Scotland (SC 038302). The Open University is authorised and regulated by the Financial Conduct Authority.